Page 142 - Mathematics Coursebook

14.3 Using direct proportion

b Weight of chicken for 4 people: 800 g
Weight of chicken for 2 people: 800 g ÷ 2 = g
Weight of chicken for 6 people: 800 g + g = g

7 Bo is paid $65 for 10 hours work. How much does she earn when she works for:
a 5 hours b 15 hours?
8 A catering company charges $960 for a meal for 120 people.
How much do they charge for a meal for:
a 60 people b 300 people?
9 This is part of Li-Ming’s homework.

Question A recipe for 6 people uses 300 g of rice.
How much rice is needed for 15 people?

Solution The recipe is for 6 people, 6 + 9 = 15
6 people need 300 g of rice
3 people need 300 g ÷ 2 = 150 g rice
6 + 3 = 9, so 300 + 150 = 450 g
Altogether 450 g of rice is needed.

Explain what she has done wrong and work out the right answer.
10 A teacher orders homework books for her class of 30 students.
The total value of the order is $135.
Two more students join her class, so she orders two extra books.
What is the total value of the order now?

Summary

You should now know that: You should be able to:
+ A ratio is a way of comparing two or more + Use ratio notation.
numbers or quantities. + Write a ratio in its simplest form.
+ The symbol : is used to show ratio. + Divide a quantity into two parts in a given ratio.
+ To write a ratio in its simplest form you divide + Recognise the relationship between ratio and
both the numbers by the highest common factor. proportion.
+ To share in a given ratio you need to: + Use direct proportion in context.
1 find the total number of parts + Solve simple problems involving ratio and direct

2 find the value of one part proportion.

3 find the value of each share. + Understand everyday systems of measurement
+ Two quantities are in direct proportion when their and use them to calculate.
ratios stay the same as the quantities increase or + Solve word problems involving whole numbers,
decrease. money or measures.

14 Ratio and proportion 141